The present invention is directed to an apparatus and method for separating constituents and, more particularly, to an apparatus and method for separating constituents in a fluid stream on the basis of differences in density or mass of the constituents by the use of centrifugal force.
Devices for separating constituents by centrifugal force on the basis of differences in density or mass of the constituents are well known in the art. The fluid stream is typically comprised of a liquid separating fluid and two or more constituents to be separated. The constituents typically comprise solids or liquids having different densities or mass.
Typically, the separation is accomplished in a cyclone separator such as the one disclosed in U.S. Pat. No. 3,802,570 to Dehne. As disclosed therein, the constituents to be separated which are intermixed in a fluid stream are fed under pressure through an inlet duct and into the interior of a stationary housing to cause the formation of a vortex in the housing. The vortex, in turn, causes the creation of a centrifugal force which causes the constituents of a lower density or mass to migrate towards the longitudinal axis of the housing and the constituent of a higher density or mass to migrate towards the inner surface of the housing. The constituent of lower density or mass is discharged through one end of the cyclone while the constituent of a higher density or mass is discharged through the opposite end of the cyclone.
The two-directional flow of the constituents in the housing resulting from the discharge of the constituents through opposite ends of the cyclone is disadvantageous because it increases the congestion of the constituents in the area of the housing where the direction of the flow of the constituents separates into an upward flow towards one end of the cyclone and a downward flow towards the opposite end of the cyclone. As a result, there is increased contact among the constituents of the fluid stream. Also, the fluid turbulence within the cyclone adds to the mixing of the constituents. In turn, it is believed that constituent interaction and increases in turbulence correlate to a decrease in efficiency of constituent separation.
Further, cyclone separators become inefficient when constituents comprising very fine particles (i.e., of less than 100 microns) are separated. Attempts to improve the efficiency of separation by only increasing the intensity of the centrifugal force (i.e., by increasing the velocity of the fluid stream being fed into the housing), disadvantageously diminishes the time which the constituents reside within the housing since the residence time is inversely proportional to the velocity of the fluid stream. Further, turbulence within the housing is disadvantageously increased due to the increased velocity of the fluid stream through an inlet duct whose size is not varied in response to the increase in fluid flow therethrough. Also, attempts to increase centrifugal force while maintaining residence times, via reducing the size of the inlet duct while keeping volumetric flow constant, disadvantageously increases turbulence. Therefore, the efficiency of separation is actually decreased when the centrifugal force is increased due to the reduction in residence time and increase in turbulence.
Alternatively, separation of constituents has, in the past, been accomplished in a rotary separator including a rotating housing rather than a stationary housing as disclosed in the above-identified cylone separator. In the rotary separator, the fluid stream is gravity fed into the rotating housing. Thereafter, the stream is forced into a circular flow pattern by the friction of the stream against the inner surface of the rotating housing. The centrifugal force which develops within the housing, as a result of the circular force of the constituents, causes the constituents to separate in a manner similar to that described with respect to the cyclone separator. However, and unlike a cyclone separator, the constituents which have been separated are, typically, discharged through the same end of the separator.
As with the cyclone separator, when one attempts to improve the efficiency of separation by increasing the intensity of the centrifugal force (i.e., by increasing the rate of rotation of the housing), the residence time of the constituents within the housing may be disadvantageously decreased thereby contributing to a reduction in the efficiency of separation.
In rotary separators, the efficiency of separation is additionally adversely affected (i.e., reduced) by the differential rotational velocities that are present across a given radial section of the interior of the housing due to the high centrifugal force action on the fluid stream. The differential rotational velocities contribute to increased turbulence within the housing which, in turn, has a disadvantageous effect on the efficiency of separation.